Jet propulsion unit comprising pulse jet units having ejector tubes within a ramjet unit



May 13, 1958 F. G. PARIS AL ,1

JET PROPULSION UNIT COMPRIS PULSE JET UNI HAVING EJECTOR TUBES WITHIN A RAMJET UNIT Filed June 5, 1951 JET PROPULSEON UNIT COMPRISING PULSE JET UNITS HAVING EJECTOR TUBES WITHIN A RAMJET UNIT Frangois G. Paris, Chaville, Jean Le Foll, Le Pro-Saint- Gervais, and Jean Bertin, Neuilly-sur-Seine, France, assigncrs to Societe Nationale dEtude et de Construction de Moteurs dAviation, Paris, France, a company of France Application June 5, 1951, Serial No. 229,946 Claims priority, application France October 7, 1950 2 Claims. (Cl. 6035.Q

The known jet propulsion units are divided into three types: jet units which employ a rotating air compressor, which are known as turbo-jet units or engine-jet units, according to whether the driving of the compressor is a piston engine; ram-jet units,

greater than the inlet velocity; and finally pulse jet units, which comprise a pulsatory combustion chamber and a nozzle which ejects the gases intermittently.

The jet units of the first type have the inconvenience that they are complicated and expensive in construction and that they wear relatively quickly.

Although the ram-jet units, which are infinitely more simple and less costly, provide a good propulsion output at high speeds, they nevertheless suflfer the disadvantage that they do not give any thrust when stationary and consequently require various expedients for launching the machine to be propelled.

Finally, the pulse jet units, which are simple and inexpensive to make, are only suitable for relatively low flying speeds.

The object of the present invention is a particular combination of a ram jet duct or nacelle and a plurality of pulse jet units, such that it is possible to obtain, with the pulse jet units, a considerable thrust when stationary and consequently the self-starting of the machine to be propelled, while the propulsion output of the ram jet unit is used at high speeds.

In this combination, the pulse jet units are disposed within the ram jet duct in such a manner that the supply of the pulse jet units takes place with air at reduced speed which has traversed the ramming intake of the ram jet duct, this offering the advantage of allowing the use of a shorter air intake tube for the pulse jet unit than in the case where the latter is fed directly with air at the forward velocity of the unit. The supply tubes of the pulse jet units are preferably of the type operating with aerodynamic valves, such as those described in our U. S. Patent application Serial No. 56,582, filed on October 26, 1948, now Patent No. 2,670,011, issued February 23, 1954. Moreover, the combustion chamber of the pulse jet units is entirely situated in the central portion or intermediate space of greater cross-section of the ram jet duct (the region where the inlet of fuel and the combustion take place in ordinary ram jet units) in such manner that the heat transmitted through the wall of the combustion chamber of the pulse jet units and which is normally lost is employed to heat ram jet cycle; finally, the outlet opening for the gases from the pulse jet units is so disposed with respect to the outlet opening of the ram jet unit that these gases react directly on the outside atmosphere or, as is possible ates Patent 6 2 in the case where there are several pulse jet units, the exhaust of the latter takes place inside the ram jet duct, a little in front of the outlet opening of the said duct.

There is thus obtained a complete and self-contained propulsion unit having considerable thrust when stationary and a satisfactory thrust characteristic as a function of the speed.

It is convenient to provide for the exhaust of the pulse jet units to take place through an ejector tube taking air from the inside of the ram jet duct and fashioned so that-this air receives a range of action of the composite jet propulsion unit is improved. Moreover, in the combination under discussion, this arrangement allows the use of pulse jets at high flying speeds and consequently they are able to add their effect over a long range of speeds to that of the ram jet.

The ejector tube, which has been described in application Serial No. 229,947 filed on June now abandoned, by the applicants is of particular interest in this respect, since it permits of the dilution air being taken up in the upstream-downstream direction of flow, thus avoiding the inversions of speed which are the patent 5, 1951,

produced when the dilution air is introduced through the outlet opening of the pulse jet unit.

The tests carried out by the applicants on pulse jet units have enabled them to determine that it is possible to take away externally some of the heat at the walls of the combustion chamber without impairing their functioning or reducing the thrust which is produced. It is thus possible to remove 40% and even 60% of the total calorific energy released by the combustion of fuel introduced into the pulsejet unit. This fact is put to advantage according to the invention for heating the air which traverses the ram jet duct. This heating may be improved by providing the outside walls of the pulse jet units with fins. The feeding of the pulse jet units through aero-dynamic valves without any movingparts has its real advantage in the fact that there is no element carrying out a reciprocatory movement. In the combination under consideration, the disadvantage which these aerodynamic valves normally have, namely, of allowing part of the gases to escape, is avoided, because it is possible to use, for heating the air of the ram jet duct, the heat carried along by these gases escaping in the opposite direction. A bent tube for turning the hot gases back into the air flow of the ram jet duct may be placed in front of each inlet tube of the pulse jet units.

Other details will be apparent from the following description taken in conjunction withthe accompanying drawing which is given by way of example, it being understood that both the details described and those shown in the drawing form part of the invention.

Figure 1 is an axial section of one embodiment of a combined propulsion unit according to the invention.

Figure 2 is a transverse section on the line II-II of Figure 1.

Figure 3 is a crosssection of a modification with three pulse jet units.

Figure 4 is a longitudinal section of another modification in which the ram jet duct has a flattened form and contains several pulse jet units in line (the axes of the pulse jet units disposed in the same plane).

Figure 5 is a transverse sectional view on the line Vl-VI of Figure 5 of such an apparatus.

Figure 6 is a section of the outlet nozzles in a modi fication.

In the embodiment shown in Figures 1 and 2, the com I nacelle 1, assumed in this example to be of circular sec tion, having its air inlet orifice at 2 and its propulsive nozzle at 3, and also four pulse jet units p p 1 p disposed next to each other within this nacelle. The maximum cross-section and the number of pulse jet units are suitably selected: according to the section of the ram jet duct in such manner that there are spaces between the pulse jet units and also between the latter and the internal wall of the nacelle 1 of the ram jet duct in order to allow the fiow of air of the ram jet duct around the pulse jet. units so as to distribute the heat transmitted externally by the pulse. jet units to the air of the ram jet duct.

Each. of the" pulse jet units comprises: an air inlet tube 4: taking in air: in the: ram jet. duct at the place where this air, which enters at Zat the forward. velocity of the unit, has been slowed down, that: is to: say, after the ramming intakefi of the nacelle: 1; a combustion chamber sinwhich is effected the pulsatorycombustion of a. fuel. introduced into: the front portion of this chamber or, more generally, towards the rear. of the tube 4. This fuel may be admitted in a continuousmanner, asis well known, the pulsatory combustion being regulated. at the frequency of the sound pipe formed by the casingof the pulse jet unit; an exhaust pipe-7 forthe ejection and the accelerationof the gases produced with each combustion; an.

ejector tube serving for the dilution and the exhaust ofthe gases to atmosphere, as described in the aforementioned patent application Serial No. 229,947, comprising lowing immediately after the exhaust pipe 7' but separated from it by an annular-orifice 9* with a convergent entrance for the inlet ofthe dilution air. application, this ejector' tube isfilled with air at the depression that follows eachdischarge of gas and this air i'sforced by the gases of the foliowing explosion which transmit to-it a part oftheir momentumin-increasing the thrust, the thrust supplementbeing assisted by the divergent section The dilution air entering by the annular orifice 9 is here taken from withinthe ram jet duct. The outlet orifice 10 for the gases and the dilution airi's a little to the rear of the outlet opening 3 of the ramjet duct, so

that the final exhaust off the pulse jet units takes place directly to atmosphere.

Thus advantage is taken of the property of pulse jet units of being able to operate pulse-jet units took place at which, in the, ordinary ram jet units, the atomisation' and combustion of fuel normally takeplace. Thus, the heat source of the combined apparatus is constituted by the part of the-heat evolved in the combustion chambers 6 of the-pulse jetunits, which is transmitted through'the walls of thesecliambersi As mentioned in the introduction, this-transmitted heat may be very considerablewithout prejudicing the functioning of the pulse jetunits. Its transfertothe air circulating in'the: ram jet duct will be improved by fins 11 (Figure 2) arranged on the-outside of the chambers 6, certainof'these fins 12" being "adapted to form partitions connecting the pulse jet' units to one another and also'securing them to the internal wall of the fairing 1.

Theinlet air tubes 40f the pulse jct units are provided with uni-directional flow control means for allowing free how toward the combustion chambers 6 While hindering back-flow therefrom. These means are conveniently of the stationary type, and'operate in a purely aerodynamic way, without any movable parts suchas flap valves. Such aerodynamic valves for pulse-jet units have been dethe said ejector tube beingmade a divergent section Sfol- As set out in the said at a fixed-setting-so as to supply, for the take-oifj all the thrust of which they are capable; without the danger of damping, which could be scribed in the above-mentioned patent application, Serial No. 56,582. However, as such tubes always allow the escape of a small part of. the high temperature gases formed by each combustion in the chamber 6, it is advantageous to use these gases for the heating of the ram jet duct. For this purpose, it is possible to place, in

i front of each of the tubes 5, a tube section 13 which is bent through in order to bring these gases back into the flow of the ram jet duct. These recuperator tubes usually have a diameter smaller than that of the inlet tube 4. and are placed at a certain distance from this tube in order not to obstruct the admission of air through the said-tube.

The apparatus thus formed is a complete and self-contained propulsion unit of. outstanding simplicity. An aircraft equipped with one or more of these apparatus is capable of taking off on its own Without any take-off aids. Moreover, at high flying speeds, the considerable thrust of the ram jet is employed, while the pulse jet units maintain av considerable thrust by means of the dilution nozzle 8. i

Itis possible to provide numerous modifications of the arrangements which have been described. 1

In particular, there is no limitation to the number of pulse jetunits. Instead of using four pulse jet units, as in. Figures 1 and 2,, it is possible to provide a greater or smaller number of. these units. Figure 3 shows an apparatus havingthree pulse jet units.

The shape of the section: of the-ram jet duct can also vary.

Inparticular,- shape allowing, arrangement of the pulse jet units along a line or parallel lines. Figures-4 and 5 illustrate the case of-a ram jetduct. with atvery flat fairing containing a set of pulse jet units 1,. 122, p p arranged along a line. Such a ram jet duct can be fitted up in an aircraft wing, its airinlet being located on the leading edge of the wing, and its outiet in the vicinity of the trailing edge.

On the other hand,cxperiments performed by the applicants have shown that when there are several pulse jet units in the fairing of the ram jet duct, these pulse jet units are coupled automatically by making their explosions follow at regular intervals. For example, two pulse jet units are coupled in phase opposition, three pulse jet units operate with a difference in phase of 3 and1(2n+1-) units at 21! 2n+1 (n being an integer), it being convenient to have an odd number of pulse jet units. The multiplicity of pulse jet unit's thus makes it' possible to obtain a quasi-permanent but variable exhaust'fiow. It is therefore possible to arrange the exhaust orifice of these pulse jet units inside the ram jet duct and a little before the outlet orifice of this duct without interfering either with the operation of the pulse jet units or with that of the'ram-jet duct.

An embodiment of this type is shown in Figure 6. The outlet orifice 3-of the ram jetduct is of such dimensionsas to allow at the same time the combined exhaust flow of the-pulse jet units and the flow of the ram jet duct. Additional heating means, e. g. fuel injectors 14, may be. disposed within the ram jet nacelle in order to heat the air performing the ram jet cycle, through combustion of .fuel therein; This results in a rise in temperature of this air andtherefore an increased thrust.

What'we claimis:

l. A- composite jet propulsion engine comprising aram jet nacelle ending-with a rearwardly facing nozzle, a

it is possible to resort to a flattened in spaced relation with said nozzle and ending substantially in a transverse plane close to the outlet of said nozzle, at least the major portion of said ejector tubes being surrounded by air flowing through said nacelle, and means for injecting fuel into the airstream flowing through the ram jet nacelle, upstream of the ejector tubes.

2. Engine as claimed in claim 1 wherein the ejector tubes end in a transverse plane located upstream of the nozzle outlet.

References Cited in the file of this patent UNITED STATES PATENTS 2,375,180 Vigo May 1, 1945 2,439,273 Silvester Apr. 6, 1948 6 Pierce Sept. 20, 1949 Bohanon Nov. 13, 1951 Johnson Mar. 11, 1952 Clayton Apr. 8, 1952 Tenney et a1. Oct. 7, 1952 Tenney et a1. Oct. 7, 1952 Kollsman Oct. 14, 1952 Stuart May 26, 1953 Marnay Apr. 13, 1954 Ballauer et al. Apr. 3, 1956 FOREIGN PATENTS Great Britain Dec. 16, 1946 Great Britain Feb. 5, 1948 

